As a car pulls up to a checkpoint in Iraq, wary
American soldiers scan driver and passengers, wondering if one of them is
preparing to fire a hidden gun.

As VIPs line up for a reception with the President and foreign leaders,
impassive security guards look each person up and down, alert to any clue
of malicious intent.

Rick Blum, professor of electrical and computer
engineering, hopes to equip these soldiers and security guards with a
device that can save them a few potentially life-saving seconds in the
search for concealed weapons.

Blum and his graduate students have devised a system that combines a
photo taken by an optical camera with a photo of the same subject taken by
a millimeter-wave camera (MMW). The result is a composite photo that
exposes much more than either photo reveals by itself.

Blum's web page for the Signal Processing and
Communication Research Lab illustrates this application of
"image fusion" with a striking set of three photos, arranged side by side,
each showing the same shot of the same three men. In the left image, taken
with an optical camera, you can see the men's faces and clothing. In the
center image, taken with an MMW camera you see no physical features or
clothing, but you can peer past their clothing and see that the man on the
right has a gun underneath his sweater.

On the right is the fused image, which police and military personnel
are seeking. Here, you see enough of the men's clothing and features to
tell them apart. You can also make out the unmistakable outline of a gun
under the third man's sweater.

Blum's work was featured on July 8, 2003 in an article
published as one of the leading stories on ABCNEWS.com.
The article was titled "Revealing Pair of Eyes: New Software Blends Images
to Spot Hidden Weapons."

Image fusion has found other applications. Using only a digital camera,
for example, Blum and his students have fused two photos of the same
setting so that an alarm clock in the foreground and a man seated in the
background are both in focus.

Blum's research group has developed new image-fusion algorithms that
perform better than all existing approaches. They are one of the few
groups to perform careful performance analysis and classification of
existing approaches. Recently, Blum and his students have begun
preliminary studies of a portable image-fusion system using wireless
communication links.

Blum, whose research specialties are wireless communications and signal
processing, originally had no intention of making a foray into
concealed-weapon detection. Eight years ago, however, while doing research
at the U.S. Air Force Research Laboratory in Rome, N.Y.,
he met researchers from the Georgia Institute of Technology who were
studying sensors for a law-enforcement client. Blum quickly saw a natural
fit between signal processing and sensors. He also met police, who
described their need for a single image that would reveal both weapon and
scene, thus enabling them to make best use of their knowledge and
experience in quickly assessing a situation.

Blum's research has been supported by the National Science Foundation, the State of
Pennsylvania, AT&T, the U.S. Army Research Office, the Office of
Naval Research and the Air Force Office of Scientific Research. He is
seeking additional funding to construct a portable image-fusion system
using wireless communication links.

With a portable system, the guards on duty at the presidential VIP
reception could scan the fused and rapidly transmitted images of arriving
guests unobserved, from a hidden room and in real time.

Another advantage of Blum's system is that, unlike x-rays, MMW cause no
physical harm to a person and can thus be taken without a person's
permission or knowledge.

One obstacle Blum has encountered is cost. MMW cameras are far too
expensive for the typical police department budget; in fact, there are
only a handful of the cameras in the U.S. Advances in sensor are very
likely to overcome this problem. As an alternate approach, Blum has
investigated using infrared sensors in place of MMW cameras. Thus far the
deficiencies of the infrared sensors have hindered progress but his
efforts continue.

In Blum's algorithms, image fusion is accomplished in the wavelet
transform domain. The two images to be fused are first processed with a
wavelet transform. Fusion is then accomplished by combining the wavelet
transforms, and the fused image is obtained by applying an inverse wavelet
transform. Blum's research group was the first to provide a very
general description of the class of algorithms of this type. Fusing the
images in the wavelet transform domain avoids the problem of incompatible
pixels, which can result when images are fused in pixel domain.

Blum sees a growing need for concealed weapons detection in Iraq, where
more than 40 American soldiers have been killed, many at checkpoints,
since major hostilities ended in April.

"It would really be great to be able to give this technology to police
and to military troops in Iraq," Blum says, "so they can determine as
quickly as possible whether or not there is an issue."

Blum is co-writing a book called Multi-Sensor Image Fusion and
Its Applications for the publisher Marcel Dekker.